The present invention relates to an assembly comprising a safety support device for a syringe and a syringe having a body presenting a collar, a piston, and a needle, the device comprising a support sheath for the syringe body and safety means comprising an inner sheath capable of sliding relative to the support sheath between a waiting, refracted position in which it is substantially retracted inside the support sheath and is suitable for being placed around at least an end portion of the syringe body carrying the needle, and a protective, extended position in which it projects beyond the support sheath to provide protection around the needle, the device further comprising retaining means suitable for being activated to retain the inner sheath in the waiting, retracted position inside the support sheath and for being deactivated to allow the inner sheath to be extended under drive from thrust means.
U.S. Pat. No. 5,492,536 shows an assembly in which a protective shield is formed by resilient strips placed around the syringe body and initially retained in a waiting position by detachable retaining means. At the end of its stroke, the piston detaches these retaining means and under drive from a thrust spring, the shield advances over the syringe body in such a manner that the strips close around the needle.
That system operates only if it is handled properly, it being necessary for the user to take care that the position of the user's fingers on the syringe does not impede movement of the shield. In addition, the strips run the risk of pinching the patient's skin as they close around the needle.
U.S. Pat. No. 5,562,626 shows a system in which the sheath is in the form of a tube retained on a collar of the syringe by resilient tabs. At the end of its stroke, the piston detaches these tabs from the collar, thus enabling the syringe body to be retracted inside the sheath body. In that case also, safety is guaranteed only if the user handles the system with care. The user holds the system via the sheath, generally gripping it between the index and middle fingers, while pressing in the piston with the thumb. The syringe body can be retracted only if the user moves the thumb away from the sheath far enough to allow the needle to be retracted fully into the sheath.
European patent application No. 0 405 039 presents a system of the same type, presenting substantially the same drawbacks.
Document EP 0 966 983 describes an assembly comprising a safety support device for a syringe and a syringe in which the body is supported in the support sheath in such a manner as to be movable relative thereto. It is this movement which, at the end of injection, serves to trigger extension of the inner sheath. To give rise to this movement, the operator must exert considerable pressure on the syringe after injecting the substance contained therein, thereby causing the needle to penetrate further and running the risk of being painful or even dangerous for the patient.